This invention concerns the measurement of pressure within a body cavity. More specifically, this invention relates to novel sealing devices for use with a fluid filled pressure catheter enclosed within a guide tube for introduction into a body cavity.
Fetal monitoring is a standard procedure for monitoring the condition of a fetus during childbirth. In most cases, fetal heart rate and intrauterine pressure are measured and separately plotted on a strip-chart recorder. By examining these curves, the onset of certain distress conditions can be detected so that appropriate remedial action can be taken earlier than would otherwise be possible.
To measure intrauterine pressure a catheter may be inserted into the uterus and filled with liquid so that the force of the intrauterine contractions can be transmitted through the uterine fluids and the liquid in the catheter to a pressure-measuring device such as a strain gauge or the like.
An intrauterine pressure catheter which may be used effectively to make measurements of uterine contractions is disclosed in U.S. Pat. No. 4,136,681 in the name of Edward H. Hon which is assigned to the assignee of the present application. U.S. Pat. No. 4,136,681 discloses an elongated catheter filled with liquid and having a perforated body end adapted to be inserted through the vagina and cervix of a woman in labor to measure intrauterine pressure. The end of the catheter opposite the body end, the gauge end, is adapted to be connected to a transducer. A curved guide tube fitted over the body end of the catheter is adapted to introduce the catheter through the woman's vagina.
At the time of manufacture, the guide tube is filled with a sterile liquid in order to minimize the likelihood of introducing air into the catheter tube during transit and use. The entire device is sealed by a suitable polymeric film which is water tight. The film must be punctured to permit entry of the catheter into the uterus and must be torn along its length to permit removal of the guide tube from around the catheter. The principal drawback of the device is that it is relatively difficult and expensive to manufacture.
U.S. Pat. No. 4,252,131, in the names of Edward H. Hon and Carmelo Dali, assigned to the assignee of the present application, discloses an improved catheter for measuring intrauterine pressure wherein the guide tube is scored along its length in two score lines and a tab is affixed to the portion of the guide tube defined by the score lines so that at the time of use, the tab may be separated from the catheter to hold the portion of the guide tube so defined away from the tube. This defines a longitudinal slot through which the catheter can pass so that the guide tube may be removed therefrom.
An outer tubular sheath or envelope receives the catheter within the guide tube and the entire assembly is filled with liquid. The envelope is sealed at its maternal end by a plug, while the gauge end of the envelope is sealed above the gauge end of the guide tube with a hollow elastomeric plug disposed about the circumference of the catheter and compressably fitted into the gauge end of the envelope. A cylindrical friction collar is slid over the envelope to compress the plug to form a liquid tight seal and to prevent relative axial movement of the catheter, guide tube and envelope.
When it is desired to apply the catheter to a patient, the envelope must first be removed from the catheter-guide tube assembly. The friction collar is displaced by turning it and sliding it axially toward the maternal end of the envelope, thereby relieving the pressure on the plug. The latter can then be removed from the envelope and from the catheter via a slit in its wall. The catheter-guide tube assembly is then removed from the envelope for insertion through the vaginal canal of the patient.
In the prior art it was thought necessary to maintain the maternal end of the guide tube sealed until after it had been inserted through the vaginal canal to a point adjacent the cervix. Accordingly, the maternal end of the guide tube was scored at two intersecting lines so that the catheter could be pushed therethrough and beyond into the uterus through the cervix in order to insure that fluid would remain in the catheter.